Papillomaviruses infect a wide variety of different species of animals including humans. Infection is typically characterized by the induction of benign epithelial and fibro-epithelial tumors, or warts at the site of infection. Each species of vertebrate is infected by a distinct group of papillomavirus, each papillomavirus group comprising several different papillomavirus types. For example, more than sixty different human papillomavirus (HPV) genotypes have been isolated. Papillomaviruses are highly species-specific infective agents. For example, canine and rabbit papillomaviruses cannot induce papillomas in heterologous species such as humans. Neutralizing immunity to infection against one papillomavirus type generally does not confer immunity against another type, even when the types infect a homologous species.
In humans, papillomaviruses cause genital warts, a prevalent sexually transmitted disease. HPV types 6 and 11 are most commonly associated with benign genital warts condyloma acuminata. Genital warts are very common and subclinical or inapparent HPV infection is even more common than clinical infection. While most HPV induced lesions are benign, lesions arising from certain papillomavirus types, e.g., HPV-16 and HPV-18, can undergo malignant progression. Moreover, infection by one of the malignancy associated papillomavirus types is considered to be a significant risk factor in the development of cervical cancer, the second most common cancer in women worldwide. Of the HPV genotypes involved in cervical cancer, HPV-16 is the most common, being found in about 50% of cervical cancers.
In view of the significant health risks posed by papillomavirus infection generally, and human papillomavirus infection in particular, various groups have reported the development of recombinant papillomavirus antigens and their use as diagnostic agents and as prophylactic vaccines. In general, such research has been focused toward producing prophylactic vaccines containing the major capsid protein (L1) alone or in combination with the minor capsid protein (L2). For example, Ghim et al, Virology, 190:548-552 (1992) reported the expression of HPV-1 L1 protein using a vaccinia expression in Cos cells which displayed conformational epitopes and the use thereof as a vaccine or for serological typing or detection. This work is also the basis of a patent application, U.S. Ser. No. 07/903,109, filed Jun. 25, 1992 (abandoned in favor of U.S. Serial No. 08/216,506, filed on March 22, 1994), which has been licensed by the assignee of this application. Also, Suzich et al, Proc. Natl. Acad. Sci., U.S.A., 92:11553-11557 (1995) report that the immunization of canines with a recombinant COPV expressed in a baculovirus/insect cell system completely prevented the development of viral mucosal papillomas. These results are important given the significant similarities between many HPVs and COPV. For example, COPV, similar to HPVs associated with anogenital and genital papillomas cancer, infects and induces lesions at a mucosal site. Also, the L1 sequences of COPV shares structural similarities to HPV L1 sequences both at the level of DNA and protein. Given these similarities, the COPV/beagle model is useful for investigation of L1 protein containing vaccines, e.g., investigation of the protective immune response, protection from natural infection and optimization of vaccination protocols. (Id.)
Also, a research group from the University of Rochester reported the production of human papillomavirus major capsid protein (L1) and virus-like particles using a baculovirus/insect cell expression system. (Rose et al, University of Rochester, WO 94/20137, published on Sep. 15, 1994). In particular, they reported the expression of the L1 major capsid protein of HPV-6 and HPV-11 and the production of HPV-6, HPV-11, HPV-16 and HPV-18 virus-like particles.
Further, a University of Queensland research group also purportedly disclosed the recombinant manufacture of papillomavirus L1 and/or L2 proteins and virus-like particles as well as their potential use as vaccines. (Frazer et al, WO 93/02189, published on Feb. 4, 1993).
Still further, a United States government research group reported recombinant papillomavirus capsid proteins purportedly capable of self-assembly into capsomere structures and viral capsids that comprise conformational antigenic epitopes. (U.S. Pat. No. 5,437,951, Lowy et al, issued on Aug. 1, 1995.) The claims of this patent are directed to a specific HPV-16 DNA sequence which encodes an L1 protein capable of self-assembly and use thereof to express recombinant HPV-16 capsids containing said HPV-16 L1 protein.
With respect to HPV capsid protein containing vaccines, it is widely accepted by those skilled in the art that a necessary prerequisite of an efficacious HPV L1 major capsid protein-based vaccine is that the L1 protein present conformational epitopes expressed by native human papillomavirus major capsid proteins (See, e.g., Hines et al, Gynecologic Oncology, 53:13-20 (1994); Suzich et al, Proc. Natl. Acad. Sci., U.S.A., 92:11553-11557 (1995)).
Both non-particle and particle recombinant HPV L1 proteins that present native conformational HPV L1 epitopes have been reported in the literature. It is known that L1 is stable in several oligomeric configurations, e.g., (i) capsomeres which comprise pentamers of the L1 protein and (ii) capsids which are constituted of seventy-two capsomeres in a T=7 icosahedron structure. Also, it is known that the L1 protein, when expressed in eukaryotic cells by itself, or in combination with L2, is capable of efficient self-assembly into capsid-like structures generally referred to as virus-like particles (VLPs).
VLPs have been reported to be morphologically and antigenically equivalent to authentic virions. Moreover, immunization with VLPs has been reported to elicit the production of virus-neutralizing antibodies. More specifically, results with a variety of animal papillomaviruses (canine oral papillomavirus and bovine papillomavirus-4) have suggested that immunization with VLPs results in protection against subsequent papillomavirus infection. Consequently, VLPs composed of HPV L1 proteins have been proposed as vaccines for preventing diseases associated with human papillomavirus infections.
Additional studies have examined the effects of L1 deletions on capsid assembly. For example, Paintsil et al recently reported that certain carboxy-terminal residues of the BPV-1 L1 protein are not required for capsid formation. (Paintsil et al, Virol., 223:238-244 (1996)). Moreover, at page 239, a schematic summary of the results obtained upon expression of various BPV L1 deletions generated by PCR mutagenesis is provided. In particular, this summary indicates whether such fragments result in proper (icosahedon) capsids, aberrant capsids, unstructured L1 aggregates or capsomeres. (Id.) Also, Paintsil et al teach a specific carboxy-deletion wherein residues 451-495 (.DELTA.C1) of the BPV-1 L1 protein were deleted. However, there is no indication that the resultant capsomeres present conformational epitopes of native BPV-1 or whether they elicited neutralizing antisera. Also, Paintsil et al (Id.), further notes at page 21, that "these truncation results suggested that deletion of a more conserved region upstream of [amino acid] 471 (FIG. 4) completely perturbs the proper folding of the L1 protein". Therefore, these results would teach against making modifications involving significant carboxy-terminal deletions. Also, their experiments are limited to BPV-1 L1 deletions and mutations.
Therefore, notwithstanding what has been previously reported, there still exists a need in the art for novel HPV major capsid protein containing compositions that present conformational epitopes associated with native (wild-type) HPVs, and methods for their manufacture.